Earthquake assessments in the national stocktake of hospital buildings have failed to use the most up-to-date engineering guidelines.
The government is advising others to use the new guidelines to assess and retrofit concrete buildings, even though they are not mandatory yet.
They are primarily a response to the poor performance of pre-cast concrete multi-storey floors in the big Kaikōura earthquake.
But the government's first-ever stocktake of 1200 hospital buildings - released this week - has used the old, mandatory assessment technical guidelines, called the Red Book.
That was because the new guidelines, called the Yellow Chapter, were "still being tested before being incorporated into regulation", the Ministry of Business, Innovation and Employment (MBIE) said.
Assessments using the Yellow Chapter have scored some buildings radically lower for quake strength, than assessments that used the Red Book did. This includes the Wellington Central Library, which has closed as a result.
Some building owners had shown "confusion" over the two versions of the guidelines, and this might have delayed some retrofits being completed, MBIE said.
Since it was released in November 2018, MBIE has been telling the industry that the Yellow Chapter was useful for figuring out how a building will perform in a quake, outside of quake-prone regulations; but to use the Red Book for official quake-prone assessments.
"Use the Yellow C5 version for seismic assessments of concrete buildings generally," MBIE told the industry.
"This version represents the most up to date engineering knowledge.
"The only time the Red version is appropriate is when you are establishing whether or not a building is earthquake prone under the Building Act 2004.
"Use Yellow C5 to inform retrofit design decisions."
Many of the hospital buildings are not suspected of being quake-prone, so the Yellow Chapter could be used.
Out of 1229 hospital buildings rated, 105 are quake-prone (or under 34 percent of New Building Standard, or NBS).
District health boards (DHBs) in quake-prone areas would be helped to do additional assessments using the Yellow Chapter, the MBIE said.
"We are working to support DHBs to get Detailed Seismic Assessments of buildings."
Engineering researchers have only just started looking at the impact on precast floors of assessing them using the Yellow Chapter, under what is called the 'C5 Evidence Project'.
That's despite these floors being the major concern after the Kaikōura quake.
They have picked six test-case buildings of different ages and characteristics.
In the first place they studied how the assessment of the primary structure varies under the old and new methods.
The results "were generally similar" overall, but individual components could vary, the MBIE said.
Work on the real focus, floors, has begun and is expected to be completed in November.
With the rules in flux, some engineers are known to be proceeding cautiously with new assessments.